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SubjectRe: Problem with kvm on -tip
Hi,

On Sat, Apr 11, 2009 at 03:08:55PM +0300, Avi Kivity wrote:
>
> This might be fixed by the attached patch.

I confirm that the patch you sent removes the warnings but does it really solve
the issue? (Sorry, I really do not know this code so I might be saying something
really stupid.)

What I understand from your patch is that the only portion of code that needs
protection is the __get_cpu_var(). If this is true then a patch like the one
below would do a better job. But I am not sure that nothing else needs
protection since the code immediately following the preempt_enable (in your
patch) is an invocation to local_irq_save()...

---
arch/x86/kvm/x86.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ca100a..cf918b5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -626,13 +626,17 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
unsigned long flags;
struct kvm_vcpu_arch *vcpu = &v->arch;
void *shared_kaddr;
+ uint32_t tsc_khz;

if ((!vcpu->time_page))
return;

- if (unlikely(vcpu->hv_clock_tsc_khz != __get_cpu_var(cpu_tsc_khz))) {
- kvm_set_time_scale(__get_cpu_var(cpu_tsc_khz), &vcpu->hv_clock);
- vcpu->hv_clock_tsc_khz = __get_cpu_var(cpu_tsc_khz);
+ preempt_disable();
+ tsc_khz = __get_cpu_var(cpu_tsc_khz);
+ preempt_enable();
+ if (unlikely(vcpu->hv_clock_tsc_khz != tsc_khz)) {
+ kvm_set_time_scale(tsc_khz, &vcpu->hv_clock);
+ vcpu->hv_clock_tsc_khz = tsc_khz;
}

/* Keep irq disabled to prevent changes to the clock */
--
1.6.2.1


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